The study is a double-masked, randomized, placebo-controlled clinical trial with a 2X2 factorial design. The goal is to assess the efficacy of antioxidant vitamins E and C on lipid peroxidation. The study is conducted at the Outpatient General Research Center in the Johns Hopkins Hospital and the Pro-Health Clinic in West Baltimore. Study population will consist of 180 healthy adults, aged 20 years or older. Participants attend a screening visit, a randomization visit and two follow-up supplements. Participants are randomized into one of four intervention groups: (1) vitamin E supplementation alone, 400 IU/d, (2) vitamin C supplementation alone, 500 mg/d, (3) combined vitamin E (400 IU/d) and vitamin C (500 mg/d) supplementation, and (4) placebo treatment. Outcome measures (F2-isoprostane and malondialdehyde) and intermediate endpoints (total oxygen-radical absorbance capacity, lipid profiles, and serum levels of vitamin C and E) from urine and blood samples will be done in laboratories.